The measuring probe T3.3 in prior public use, order no. BO1.16.01 of the inventor's firm comes closest to the subject of the invention. Probes and parts of probes of the same generic type are described in German Offenlegungsschrift 3,437,253 and in U.S. Pat. Nos. 2,933,677, 3,761,804, 4,005,360 and 4,041,378. Such measuring probes are used, for example, to measure the thickness of varnish coatings, the layer thickness of metal layers on base metals etc. Representative layer thicknesses lie between several hundred micrometers and several tens of nanometers.
These devices are undoubtedly measuring devices which measure in a nondestructive manner.
It has, however, been noticed that inexplicable measuring errors occur during the measuring of very thin layers and it is known that, when measuring some surfaces which are polished bright, impairment of the gloss occurs in spite of nondestructive measuring.
The points on the layers to be measured on which the convex end face was placed, have been inspected and it has been seen that considerable dents occur there. In manual application, there are both dents and scratch marks, which lead from the place where the convex end face sets down to the actual measuring point. Even if these probes, which are in fact intended for manual operation, are applied carefully using a stand, for example to aluminum, there are indentations. If the aluminum is anodized, the outermost thin lay may collapse, similar to the encrusted surface on old snow when it is trodden on. A representative depth of such impressions is for example around one micrometer. If the layer is, for example, 120 micrometers thick, this of course makes relatively little difference. The thinner the layer, the greater the error. If the indentation is 1.5 micrometers and the layer to be measured is likewise 1.5 micrometers thick, a measuring error of 50% is produced by the indentation alone, to say nothing of measuring in the nanometer range.